1. Field of the Invention The invention relates to an improved method for sterilizing containers and to improved devices for executing the method.
2. Description of the Prior Art
It is sufficiently well-known in the fields of medicine or food technology to use physical or chemical methods to remove dangerous microorganisms or germs in containers, for example in ampules, septic glass containers, syringes, vials, and other so-called parenteralia packages, or in beverage bottles.
The sterilization of devices and packaging through the use of dry heat is known, for example, from WO-9839216 A1 or EP 0512244 A1.
Furthermore, in an intrinsically known steam method with an aqueous precleaning, the containers can be subjected for a predetermined time interval to hot or superheated steam. The duration of the process requires large systems in order to be able to sterilize large numbers of articles in a manner that is integrated into the production stream. This steam sterilization, however, is not able to completely remove so-called pyrogens, i.e. inflammation-inducing decomposition products and cellular residue components of dead germs.
Both of the methods mentioned above have their own specific disadvantages. The application of dry heat requires that the devices to be treated be made of temperature-stable materials, e.g. steel, ceramic, or glass. Furthermore, the heat treatment specifically in the region to be filled with parenteralia must be immediately followed by a cooling process that is expensive, particularly with regard to energy, space, and investment costs, in order to be able to be filled with temperature-sensitive materials at room temperature.
This is why chemicals are also often used for sterilization, for example peracetic acid or hydrogen peroxide in the vapor phase, e.g. known from DE 24 35 037 A1, or gaseous ethylene oxide. A treatment, for example, with hydrogen peroxide vapor does in fact produce oxidation of dead cell residue components, but requires a careful cleaning and a correspondingly high cost. Moreover, many packaging materials, for example many plastics, are not stable in the presence of hydrogen peroxide. Up to now, it has only been possible to use these two methods with glass containers, since the required temperatures are too high for plastic containers.
In addition, methods with UV radiation, known per se from DE 25 30 113 A1, or with Gamma radiation according to WO 95 33 651 A1 have proven advantageous due to their sterilizing properties and are therefore used to sterilize articles and packaging.
EP 0 377 799 A1 has disclosed a method in which a plasma is generated using an electromagnetic radiation with a frequency of approximately 2.45 GHz in order to sterilize articles. In order to achieve this, the entire article is exposed to a low-pressure plasma and in one modification, is also irradiated by an additional heat source. Up to now, sterilization by means of a plasma has mainly been used to treat medical devices, for example catheters or transfusion instruments.
The sterilization, i.e. the degradation of viable organisms, in the known methods described above is insufficient for use on articles in the medical field, for example medical instruments or the packaging of parenteralia. These applications also require that inflammation-inducing residual components, so-called endotoxins, of the dead germs also be removed or at least permanently inactivated with regard to their pyrogenic effects. This applies primarily to so-called lipopolysaccharides of Gram-negative bacteria, which are disposed on the outside of the cell wall and, when they get into the bloodstream, can provoke defensive reactions.
The provision of a sufficient endotoxin degradation through the action of heat in this instance requires an at least 300° C. container temperature and currently only suffices if there is a long heat treatment of >5 min., which is followed by an even longer cooling phase. In the case of plasma sterilization using hydrogen peroxide, the plasma is only used to remove peroxide residues from substrates. The sterilizing action is the conventional chemical action of hydrogen peroxide. The processing times are therefore correspondingly long, i.e. as a rule greater than 30 minutes.
This plasma process consequently requires a large amount of time and the use of an aggressive chemical, for example hydrogen peroxide or peracetic acid, all residues of which must be removed before further use of the devices. Moreover, special devices are required, in order, in hollow articles, to assure a sufficient germ and endotoxin degradation on the inside of the hollow articles as well, as described, for example, in U.S. Pat. No. 5,200,158 A1.
Furthermore, the scientific paper by R. E. Peeples and N. R. Anderson in the Journal of Parenteral Science and Technology, Vol. 39/1, pp. 9-15, 1985 has disclosed a method in which a microwave launch can ignite a plasma in a vial for the purpose of endotoxin degradation. In this case, the plasma was ignited with the aid of a laser flash and was only maintained for a few seconds. This produced a large temperature gradient inside the vial, e.g. 31° C. at the bottom and 1665° C. at the lip. The technical complexity with the use of a microwave source and a laser as well as the unsatisfactory guarantee of ignition, particularly with different hollow body formats, and the enormous temperature gradient are disadvantageous, particularly for use in packaging technology applications.